1. Field of the Invention
The present invention relates to a belt-type continuously variable transmission in which a metal belt is wound around a drive pulley and a driven pulley which are both variable in groove width.
2. Description of the Related Art
In a belt-type continuously variable transmission as shown in FIG. 7, a metal belt 03 is wound around a drive pulley 01 and a driven pulley 02. A fixed pulley half 04 of the drive pulley 01 and a fixed pulley half 05 of the driven pulley 02 are disposed at diagonal positions, whereas a movable pulley half 06 of the drive pulley 01 and a movable pulley half 07 of the driven pulley 02 are disposed at diagonal positions. Consequently, when the movable pulley halves 06, 07 of the drive pulley 01 and the driven pulley 02 move closer to and apart from the fixed pulley halves 04, 05, a center line La of a V-groove in the drive pulley 01 and a center line Lb of a V-groove in the driven pulley 02 come to be out of alignment with each other, producing a slight misalignment xcex1.
Known through JP-A-61-82060 and JP-A-63-106454 are belt-type continuously variable transmissions in which the drive ratio at which the misalignment between a drive pulley and a driven pulley is removed is determined from view points of the performance and efficiency of a vehicle.
Incidentally, the movable pulley half is hydraulically biased toward the fixed pulley half in such a manner that the metal belt is prevented from slipping, and therefore both the pulley halves are deformed in such a manner as to deflect axially outwardly with a reaction force exerted by the metal belt. As this occurs, in the event that the rigidity of both the pulley halves is identical, the amount of deformation thereof becomes uniform, and therefore there is no case where the magnitude of misalignment varies due to the deformation. However, in fact, since there exists a difference in rigidity between the movable pulley half and the fixed pulley half, the amount of deformation of both the pulley halves become uneven, affecting the magnitude of misalignment. In general, a cylinder is integrally formed on a back of the movable pulley half to partition a hydraulic fluid chamber thereat. Moreover, since not only a controlled hydraulic pressure for biasing the movable pulley half toward the fixed pulley half but also a centrifugal pressure generated in conjunction with the rotation of the pulley are exerted on the hydraulic fluid chamber, the rigidity of the movable pulley half becomes higher than the rigidity of the fixed pulley half.
Solid lines illustrated in FIGS. 6A to 6C indicate the variation of the misalignment relative to the change in drive ratio when the rigidity ratio of the fixed pulley half and the movable pulley half is 1 to 1. The amount of misalignment decreases from a positive value as the drive ratio increases and passes through zero to become a negative value. Thereafter, the misalignment amount increases and passes through zero again to become a positive value. The maximum and minimum values of the amount of misalignment are set such that absolute values (about 0.4 mm) thereof become substantially equal to each other.
A broken line in FIG. 6A shows a characteristic resulting when the rigidity ratio of the fixed pulley half and the movable pulley half is 1 to 1.5, and the characteristic is deviated downwardly when compared with a characteristic (refer to the solid line) resulting when the rigidity ratio is 1 to 1. A broken line in FIG. 6B shows a characteristic resulting when the rigidity ratio of the fixed pulley half and the movable pulley half is 1 to 2, and the characteristic is deviated further downwardly when compared with a characteristic (refer to the solid line) resulting when the rigidity ratio is 1 to 1. A broken line in FIG. 6C, which is shown by reference, shows a characteristic resulting when the rigidity ratio of the fixed pulley half and the movable pulley half is 1.5 to 1, and the characteristic is deviated upwardly when compared with a characteristic (refer to the solid line) resulting when the rigidity ratio is 1 to 1.
The invention was made in view of these situations and an object thereof is to make the variation characteristics of misalignment approach a characteristic set in advance by reducing the difference in rigidity between fixed pulley halves and movable pulley halves of a belt-type continuously variable transmission.
With a view to attaining the object, according to a first aspect of the invention, there is provided a belt-type continuously variable transmission comprising a drive pulley comprising in turn a fixed pulley half and a movable pulley half adapted to move closer to and apart from the fixed pulley half and supported on an input shaft, a driven pulley comprising a fixed pulley half and a movable pulley half adapted to move closer to and apart from the fixed pulley half and supported on an output shaft, and a metal belt extended to be wound around the drive pulley and the driven pulley, wherein both the fixed pulley halves and both the movable pulley halves are disposed at diagonal positions, respectively, wherein hydraulic fluid chambers are formed in both the movable pulley halves, and wherein a number of detection teeth for a rotation sensor are formed in radial directions on a back of an outer circumferential portion of at least one of both the fixed pulley halves. The detection teeth for the rotation sensor are formed in an annular protruding portion provided on the back of the outer circumferential portion of the at least one of he fixed pulley halves.
According to the above construction, since the annular protruding portion is formed on the back of the protruding portion of at least one of the drive pulley and the driven pulley of the belt-type continuously variable transmission and the detection teeth for the rotational sensor are formed in the protruding portion, the annular protruding portion can be made to contribute effectively to the enhancement of rigidity of the fixed pulley half. Then, since the difference in rigidity between the fixed pulley half and the movable pulley half whose rigidity is increased by the provision of the hydraulic fluid chamber can be reduced by the enhancement of rigidity of the fixed pulley half, the variation characteristics of misalignment relative to the drive ratio can be made to approach the characteristic which is set in advance by making the amount of deformation of both the pulley halves uniform.
In addition, according to a second aspect of the invention, there is provided a belt-type continuously variable transmission as set forth in the first aspect of the invention, wherein the detection teeth are formed by machining grooves in the annular protruding portion.
According to the above construction, since the grooves can be machined in the annular protruding portion, the detection teeth can easily be formed through the simple machining in which the grooves are spot-faced.
Furthermore, according to a third aspect of the invention, there is provided a belt-type continuously variable transmission as set forth in the second aspect of the invention, wherein the grooves are each made to open in an outer circumferential surface and a side of the annular protruding portion and terminate at a position in the annular protruding portion just before the grooves reach an inner circumferential surface of the annular protruding portion.
According to the above construction, since the annular protruding portion is provided with the grooves which are each made to open toward the outer circumferential surface and the side of thereof and terminate at the position where the grooves do not reach the inner circumferential surface thereof, the annular protruding portion can be made to contribute effectively to the enhancement in rigidity of the fixed pulley half when compared with a case in which the grooves extend through the annular protruding portion from the outer circumferential surface to the inner circumferential surface of the annular protruding portion.